Hybrid transmission

ABSTRACT

A hybrid transmission connected with a prime power source, including an input member for receiving power input from the prime power source, a two degree-of-freedom gear mechanism having a first axis and including at least four rotating members that are associated to rotate about the first axis, a first motor/generator having a second axis aligned with the first axis of the two degree-of-freedom gear mechanism, and a second motor/generator having a third axis offset from and parallel to the first axis. The first motor/generator is drivingly connected with the first rotating member of the two degree-of-freedom gear mechanism. The second motor/generator is drivingly connected with the second rotating member of the two degree-of-freedom gear mechanism.

BACKGROUND OF THE INVENTION

The present invention relates to a hybrid transmission adapted for ahybrid electric vehicle (HEV) in which multiple power sources includingan engine and a motor are provided. More specifically, the presentinvention relates to a hybrid transmission capable of continuously andvariably transmitting the power output from the power sources using adifferential device such as a planetary gear set.

U.S. Pat. No. 5,935,035 (corresponding to Japanese Patent No. 3,330,900)discloses a hybrid transmission in which rotating members constituting adifferential device are connected with a prime power source, a drivesystem and two motor/generators. The two motor/generators are arrangedin an axial direction of the hybrid transmission.

SUMMARY OF THE INVENTION

However, in the above-described related art having the two axiallyarranged motor/generators, an axial dimension of the hybrid transmissionis increased, whereby installation ability thereof to a vehicle bodywill be deteriorated. Further, in the axial arrangement of the twomotor/generators, the amount of overhang of one motor/generator unitwhich is disposed away from the prime power source is increased andsupported in the form of a cantilever. This causes deterioration of themounting strength of the hybrid transmission, thereby resulting in lackof rigidity of the entire hybrid transmission.

It is an object of the present invention to provide a hybridtransmission capable of preventing deterioration of installation abilitythereof to a vehicle body which will be caused due to an increased axialdimension thereof, and suppressing the deterioration of the mountingstrength which will be caused due to the cantilever supporting structureof one of the motor/generator unit, to thereby avoid the lack of therigidity of the hybrid transmission.

In one aspect of the present invention, there is provided a hybridtransmission comprising:

-   -   a two degree-of-freedom gear mechanism having a first axis and        including at least four rotating members that are associated to        rotate about the first axis and include a first rotating member        and a second rotating member, the two degree-of-freedom gear        mechanism being constructed such that, when rotation conditions        of any two of the at least four rotating members are determined,        rotation conditions of the remainder of the at least four        rotating members are determined depending thereon, the two        degree-of-freedom gear mechanism being adapted for receiving        power input from a prime power source and delivering power        output from the two degree-of-freedom gear mechanism;    -   a first motor/generator having a second axis aligned with the        first axis, the first motor/generator being drivingly connected        with the first rotating member of the two degree-of-freedom gear        mechanism via a hollow shaft; and    -   a second motor/generator having a third axis offset from and        parallel to the second axis, the second motor/generator being        drivingly connected with the second rotating member of the two        degree-of-freedom gear mechanism via a central shaft which        extends through the hollow shaft and the first motor/generator,    -   the first and second motor/generators being disposed on one side        of the two degree-of-freedom gear mechanism in a direction of        the first axis, the prime power source being disposed on an        opposite side of the two degree-of-freedom gear mechanism in the        direction of the first axis.

In a further aspect of the invention, there is provided a hybridtransmission comprising:

-   -   a two degree-of-freedom gear mechanism having a first axis and        including at least four rotating members that are associated to        rotate about the first axis and include a first rotating member        and a second rotating member, the two degree-of-freedom gear        mechanism being constructed such that, when rotation conditions        of any two of the at least four rotating members are determined,        rotation conditions of the remainder of the at least four        rotating members are determined depending thereon, the two        degree-of-freedom gear mechanism being adapted for receiving        power input from a prime power source and delivering power        output from the two degree-of-freedom gear mechanism;    -   a first motor/generator having a second axis aligned with the        first axis, the first motor/generator being disposed between the        two degree-of-freedom gear mechanism and the prime power source        and drivingly connected with the first rotating member of the        two degree-of-freedom gear mechanism; and    -   a second motor/generator having a third axis offset from and        parallel to the first axis, the second motor/generator being        drivingly connected with the second rotating member of the two        degree-of-freedom gear mechanism via a shaft extending from the        second rotating member in such a direction as to come away from        the prime power source.

In a still further aspect of the invention, there is provided a hybridtransmission connected with a prime power source, the hybridtransmission comprising:

-   -   an input member for receiving power input from the prime power        source;    -   a two degree-of-freedom gear mechanism having a first axis and        including at least four rotating members that are associated to        rotate about the first axis and include a first rotating member        and a second rotating member, the two degree-of-freedom gear        mechanism being connected with the input member and constructed        such that, when rotation conditions of any two of the at least        four rotating members are determined, rotation conditions of the        remainder of the at least four rotating members are determined        depending thereon;    -   a first motor/generator having a second axis aligned with the        first axis of the two degree-of-freedom gear mechanism, the        first motor/generator being drivingly connected with the first        rotating member of the two degree-of-freedom gear mechanism; and    -   a second motor/generator having a third axis offset from and        parallel to the first axis, the second motor/generator being        drivingly connected with the second rotating member of the two        degree-of-freedom gear mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematically developed and longitudinal cross-sectionalview of a hybrid transmission according to a first embodiment of thepresent invention.

FIG. 1B is a lever diagram of the hybrid transmission of FIG. 1A.

FIG. 2 is a view similar to FIG. 1A, but showing a hybrid transmissionaccording to a second embodiment of the present invention.

FIG. 3 is a view similar to FIG. 2, but showing a hybrid transmissionaccording to a third embodiment of the present invention.

FIG. 4 is a view similar to FIG. 2, but showing a hybrid transmissionaccording to a fourth embodiment of the present invention.

FIG. 5A is a view similar to FIG. 2, but showing a hybrid transmissionaccording to a fifth embodiment of the present invention.

FIG. 5B is a lever diagram of the hybrid transmission of FIG. 5A.

FIG. 6 is an explanatory diagram, as viewed from a direction of an axisof the hybrid transmission, showing an arrangement of components of thehybrid transmission which is common to the first through fifthembodiments.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1A, a hybrid transmission according to a firstembodiment of the present invention now is explained. In thisembodiment, the hybrid transmission is applied to a transaxle for afront-engine front-drive (FF) vehicle.

Hybrid transmission 100 includes transmission case 1 through which axisO1 extends, two degree-of-freedom gear mechanism 2, firstmotor/generator MG1 and second motor/generator MG2 which are installedin transmission case 1 along axis O1. As illustrated in FIG. 1A, twodegree-of-freedom gear mechanism 2 is disposed on the right side asviewed in the figure in a direction of axis O1, and first and secondmotor/generators MG1 and MG2 are disposed on the left side as viewed inthe figure in the direction of axis O1. Engine 3 acting as a prime powersource is disposed on the outside of transmission case 1 and located onthe right side of two degree-of-freedom gear mechanism 2 as shown inFIG. 1A. In FIG. 1A, there is shown only a crankshaft of engine 3 forthe purpose of simple illustration.

Two degree-of-freedom gear mechanism 2, engine 3 and firstmotor/generator MG1 are arranged coaxially with hybrid transmission 100.Namely, two degree-of-freedom gear mechanism 2, engine 3 and firstmotor/generator MG1 are arranged such that axes thereof are aligned withaxis O1 of hybrid transmission 100. In contrast, second motor/generatorMG2 is arranged in non-concentrical relation to first motor/generatorMG1. Specifically, second motor/generator MG2 is arranged offset fromfirst motor/generator MG1 such that axis O2 of second motor/generatorMG2 is offset from the axis of first motor/generator MG1, namely, axisO1, in parallel relation thereto. Countershaft 5 having axis O3 anddifferential 6 having axis O4 are disposed within transmission case 1 insuch a manner that axis O3 and axis O4 are offset from axis O1 inparallel relation thereto. FIG. 6 illustrates an arrangement of axesO1-O4. As shown in FIG. 6, axis O2 of second motor/generator MG2 andaxis O3 of countershaft 5 are positioned on both sides of plane M whichcontains axis O1 of hybrid transmission 100 and axis O4 of differential6. Thus, second motor/generator MG2 is arranged in opposed relation tocountershaft 5 with respect to plane M. In FIG. 6, reference numeral 16denotes an output gear which is arranged coaxially with hybridtransmission 100 and has a rotation axis aligned with axis O1. Referencenumeral 17 denotes a counter gear supported on countershaft 5. Referencenumeral 18 denotes a final drive pinion integrally formed withcountershaft 5. Reference numeral 19 denotes a final drive ring gearprovided on differential 6.

Two degree-of-freedom gear mechanism 2 includes at least four rotatingmembers that are associated to rotate about the axis, i.e., axis O1. Twodegree-of-freedom gear mechanism 2 is constructed such that, whenrotation conditions of any two of the at least four rotating members aredetermined, rotation conditions of the remainder of the at least fourrotating members are determined depending thereon. In this embodiment,two degree-of-freedom gear mechanism 2 is formed by a compound planetarygear set of a Ravigneaux type. Namely, the Ravigneaux compound planetarygear set is a combination of single-pinion planetary gear set 7 anddouble-pinion planetary gear set 8 in which pinion P1 and ring gear RSare common. Single-pinion planetary gear set 7 is located closer toengine 3 than double-pinion planetary gear set 8 is. Single-pinionplanetary gear set 7 includes sun gear SS and ring gear RS, with whichcommon pinion P1 meshes. Double-pinion planetary gear set 8 includes sungear SD and short pinion P2 having a diameter larger than common pinionP1. Short pinion P2 meshes with sun gear SD and common pinion P1.Pinions P1 and P2 are rotatably supported by common carrier C.

Two degree-of-freedom gear mechanism 2 includes the four rotatingmembers acting as four primary elements, i.e., sun gear SS, sun gear SD,ring gear RS and carrier C. FIG. 1B is a lever diagram showing arelationship between rotation speeds and rotation directions of the fourrotating members. As shown in FIG. 1B, the rotation speeds of the fourrotating members are in the following order: sun gear SD, ring gear RS,carrier C and sun gear SS.

As illustrated in FIG. 1A, first motor/generator MG1 includes firstrotor 4R1 disposed in transmission case 1 so as to be rotatable aboutaxis O1, and first annular stator 4S1 surrounding first rotor 4R1 andfixed to transmission case 1. Second motor/generator MG2 includes secondrotor 4R2 disposed within transmission case 1 so as to be rotatableabout axis O2, and second annular stator 4S2 surrounding second rotor4R2 and fixed to transmission case 1. First and second motor/generatorsMG1 and MG2 are substantially aligned with each other with respect tosame plane perpendicular to axes O1 and O2. Specifically, each of firstand second motor/generators MG1 and MG2 has a front end which is locatedon the side of engine 3 and supported by intermediate wall 1A oftransmission case 1. A rear end of each of first and secondmotor/generators MG1 and MG2 is opposed to rear cover 1B of transmissioncase 1 which closes a rear end opening of transmission case 1.

When an electric current is supplied to stator 4S1 and 4S2 of each offirst and second motor/generators MG1 and MG2 to thereby rotate rotor4R1 and 4R2 thereof, motor/generator MG1 and MG2 operates as a motorproducing a rotation output having a direction and a speed (includingzero) which correspond on the electric current supplied. On the otherhand, when each of rotors 4R1 and 4R2 generates an electric current instator 4S1 and 4S2 in response to an external rotation input, each offirst and second motor/generators MG1 and MG2 operates as a generatorproducing an electric power corresponding to the external rotationinput.

As shown in FIG. 1B, sun gear SD, ring gear RS, carrier C and sun gearSS of two degree-of-freedom gear mechanism 2 are connected with firstmotor/generator MG1 (first rotor 4R1), input IN from engine 3, outputOUT to a wheel driving system and second motor/generator MG2 (secondrotor 4R2), respectively. Specifically, as illustrated in FIG. 1A, ringgear RS is connected to transmission input shaft 10, serving as an inputelement to which rotation from engine 3 is input. Transmission inputshaft 10 is drivingly connected to engine 3 via clutch 11. Sun gear SDis drivingly connected with first rotor 4R1 of first motor/generator MG1via hollow shaft 13 extending toward an opposite side of engine 3. Sungear SS is drivingly connected with second rotor 4R2 of secondmotor/generator MG2 via central shaft 14 extending through an inside ofhollow shaft 13. Hollow shaft 13 and central shaft 14 are disposedconcentrically with axis O1.

Central shaft 14 extends from sun gear SS in such a direction as to comeaway from input shaft 10 and engine 3 through hollow shaft 13 and firstrotor 4R1 of first motor/generator MG1. There is a clearance between acircumferential outer surface of central shaft 14 and circumferentialinner surfaces of hollow shaft 13 and first rotor 4R1. Central shaft 14projects into rear cover 1B of transmission case 1. Central shaft 14 andsun gear SS are drivingly connected with second rotor 4R2 via atransmitting device. The transmitting device is a gear train constitutedof two gears 21 and 22 which have different diameters. Gear 21 isprovided on an end portion of central shaft 14 which projects from oneaxial end of first rotor 4R1 toward rear cover 1B. Gear 22 meshing withgear 21 is provided on an end portion of a central shaft of second rotor4R2 of second motor/generator MG2 which projects from one axial end ofsecond rotor 4R2 into rear cover 1B.

Carrier C is drivingly connected with output gear 16 via hollowconnecting member 15 which concentrically extends over hollow shaft 13and acts as an output shaft. Carrier C serves as an output elementdelivering the rotation output to the wheel driving system. Output gear16 is rotatably disposed within transmission case 1 and arranged betweentwo degree-of-freedom gear mechanism 2 and first motor/generator MG1 inthe direction of axis O1. Output gear 16 meshes with counter gear 17supported on countershaft 5. Countershaft 5 has integral final drivepinion 18 meshing with final drive ring gear 19 provided on differential6.

The rotation output from output gear 16 is transmitted to the wheeldriving system. Specifically, the rotation is transmitted todifferential 6 via counter gear 17 and a final drive gear setconstituted of final drive pinion 18 and final drive ring gear 19. Therotation output from differential 6 is distributed to left and rightdriving wheels, not shown.

Thus-constructed hybrid transmission 100 operates as follows. Asindicated by lever EV shown in FIG. 1B, when a forward or positiverotation output is transmitted, first and second motor/generators MG1and MG2 operate as motors to produce a power output for driving thevehicle without depending on the power output from engine 3. In thiscase, the electrical running of the vehicle can be attained only usingthe power of motor/generators MG1 and MG2.

Next, as indicated by lever MAX shown in FIG. 1B, when the positiverotation speed of motor/generators MG1 and MG2 and the rotation speed ofring gear RS, namely, the rotation output from engine 3, are increasedto the largest possible values, respectively, the rotation output fromcarrier C is enhanced to a maximum.

Further, as indicated by lever REV shown in FIG. 1B, when firstmotor/generator MG1 operates in the positive rotation direction andsecond motor/generator MG2 operates in a reverse rotation direction, thereverse rotation output is transmitted from carrier C to the wheeldriving system.

As described above, in hybrid transmission 100 of this embodiment, firstmotor/generator MG1 is arranged coaxially with two degree-of-freedomgear mechanism 2 and hybrid transmission 100, and drivingly connectedwith the rotating member of two degree-of-freedom gear mechanism 2,i.e., sun gear SD of double-pinion planetary gear set 8 of compoundplanetary gear set 2, via hollow shaft 13. Second motor/generator MG2 isarranged such that axis O2 thereof is offset from axis O1 in parallelrelation thereto, and drivingly connected with the rotating member oftwo degree-of-freedom gear mechanism 2, i.e., sun gear SS ofsingle-pinion planetary gear set 7 of compound planetary gear set 2, viacentral shaft 14 which extends through hollow shaft 13 and first rotor4R1 of first motor/generator MG1. Two degree-of-freedom gear mechanism 2is disposed between first and second motor/generators MG1 and MG2 andinput shaft 10 connected with engine 3. Input shaft 10 and engine 3 arelocated on one side of two degree-of-freedom gear mechanism 2 in thedirection of axis O1, and two motor/generators MG1 and MG2 are locatedon an opposite side of two degree-of-freedom gear mechanism 2 in thedirection of axis O1. Thus-constructed hybrid transmission 100 has thefollowing effects.

With the offset arrangement, two motor/generators MG1 and MG2 areprevented from being juxtaposed to each other in the direction of axisO1. This can avoid increase in dimension in the axial direction ofhybrid transmission 100 to thereby prohibit deterioration in theinstallation ability to a vehicle body. Further, second motor/generatorMG2 can be free from being supported in a cantilever form so that hybridtransmission 100 can be prevented from lacking the rigidity.Furthermore, two motor/generators MG1 and MG2 are arranged insubstantially alignment with each other with respect to the same planeperpendicular to axis O1. The axial end of each of rotors 4R1 and 4R2 ofmotor/generators MG1 and MG2 which is located on the side of engine 3,is supported on intermediate wall 1A of transmission case 1. With thearrangement, the mounting strength of first and second motor/generatorsMG1 and MG2 can be enhanced, whereby the rigidity of hybrid transmission100 can be increased.

Further, as illustrated in FIG. 6, second motor/generator MG2 andcounter gear 17 and final drive pinion 18, namely, countershaft 5, arearranged on both sides of plane M which contains axis O1 of hybridtransmission 100, namely, the axis of output shaft 15, and axis O4 ofdifferential 6, namely, the axis of final drive ring gear 19. Thisallows a well-balanced layout of the components of hybrid transmission100 in the space on both sides of plane M, serving for reducing a radialsize of hybrid transmission 100. Further, the weight balance of hybridtransmission 100 on both sides of plane M can be improved so that theinstallation stability can be enhanced.

Further, as shown in FIG. 1A, central shaft 14 connected with sun gearSS and second rotor 4R2 of second motor/generator MG2 are drivinglyconnected with each other via the gear train constituted of gears 21 and22. By suitably selecting the gear ratio of gears 21 and 22, the degreeof freedom of choice of second motor/generator MG2 can be increased.Furthermore, the suitable selection of the gear ratio allows reductionof a diameter of the shaft of second motor/generator MG2, serving forrealizing further reduction of the radial dimension of hybridtransmission 100.

Referring to FIG. 2, there is shown the hybrid transmission of a secondembodiment of the present invention. The second embodiment differs inconstruction of first and second motor/generators MG1 and MG2 from thefirst embodiment. Like reference numerals and letters denote like parts,and therefore, detailed explanations therefor are omitted. Asillustrated in FIG. 2, hybrid transmission 200 includes firstmotor/generator MG1 as explained in the first embodiment, and secondmotor/generator MG2 having an axial length longer than that of firstmotor/generator MG1 and a diameter smaller than that of firstmotor/generator MG1. The axial length of second motor/generator MG2 isnot longer than the axial length of hybrid transmission 200. Secondmotor/generator MG2 includes second rotor 4R2 rotatably supported ontransmission case 1 and annular second stator 4RS fixed to transmissioncase 1. Second stator 4RS is enclosed in motor/generator casing 4C oftransmission case 1 which is integrally formed with transmission case 1.

In this embodiment, the bearing span of second rotor 4R2 of secondmotor/generator MG2 is increased so that mounting rigidity of secondmotor/generator MG2 can be enhanced as compared with the firstembodiment. Further, motor/generator casing 4C accommodating secondmotor/generator MG2 having the longer axial length is elongated so as tooverlap that of transmission case 1. This can increase the rigidity oftransmission case 1. Further, second motor/generator MG2 having thesmaller diameter can be enhanced in response, and serves for reducingthe diameter of hybrid transmission 200 to thereby render hybridtransmission 200 more compact in size. Furthermore, secondmotor/generator MG2 having the axial length which is not longer thanthat of hybrid transmission 200 can be prohibited from interfering withengine 3.

Referring to FIG. 3, there is shown the hybrid transmission of a thirdembodiment of the present invention. The third embodiment differs inthat a wrapping connector driving member is used as a transmittingdevice for drivingly connecting central shaft 14 extending from sun gearSS with second rotor 4R2 of second motor/generator MG2, from the secondembodiment using the gear train including gears 21 and 22. Asillustrated in FIG. 3, hybrid transmission 300 includes wrappingconnector driving member 23 such as belt or chain 23C wrapped around twowheels 23A and 23B. Wheel 23A is provided on the end portion of centralshaft 14 which projects from the axial end of first rotor 4R1 into rearcover 1B. Wheel 23B is provided on the end portion of the central shaftof second rotor 4R2 which projects from the axial end of second rotor4R2 into rear cover 1B.

Referring to FIG. 4, there is shown the hybrid transmission of a fourthembodiment of the present invention. The fourth embodiment differs instructure of the gear train serving as the transmitting device fordrivingly connecting central shaft 14 and sun gear SS with second rotor4R2 of second motor/generator MG2, from the second embodiment. Asillustrated in FIG. 3, hybrid transmission 300 includes gear train 27constituted of three gears 24, 25 and 26. Gear 24 is provided on the endportion of central shaft 14 which projects from the axial end of firstrotor 4R1 into rear cover 1B. Gear 25 is connected with the end portionof the central shaft which projects from the axial end of second rotor4R2 into rear cover 1B. Idler gear 26 is interposed between gears 24 and25 in meshing engagement therewith.

In the third embodiment using wrapping connector driving member 23 andthe fourth embodiment using gear train 27, the gear ratio can be set ina wide range as compared with the first and second embodiments. Thisresults in the following effects. Specifically, in a case where secondmotor/generator MG2 having a relatively small diameter is used, thedistance between axis O1 of first motor/generator MG1 and axis O2 ofsecond motor/generator MG2 becomes smaller. In this case, if the geartrain including gears 21 and 22 of the first and second embodiments isused, a sufficient gear ratio may not be obtained. In contrast, ifwrapping connector driving member 23 of the third embodiment and geartrain 27 of the fourth embodiment are used, a desired gear ratio can berealized over a wide range. This serves for further increasing a degreeof freedom of selecting second motor/generator MG2.

Referring to FIG. 5A, there is shown the hybrid transmission of a fifthembodiment of the present invention. The fifth embodiment differs inlayout of the first motor/generator and the two degree-of-freedom gearmechanism from the second embodiment. As illustrated in FIG. 5A, hybridtransmission 500 includes first motor/generator MG1 disposed on theright side as viewed in the figure in the direction of axis O1 and twodegree-of-freedom gear mechanism 31 disposed on the left side as viewedin the figure in the direction of axis O1. Specifically, firstmotor/generator MG1 is disposed between two degree-of-freedom gearmechanism 31 and input shaft 10 connected with engine 3 in the directionof axis O1. Input shaft 10 and engine 3 are located on one side of firstmotor/generator MG1. Two degree-of-freedom gear mechanism 31 is locatedon an opposite side of first motor/generator MG1. Two degree-of-freedomgear mechanism 31, engine 3 and first motor/generator MG1 are arrangedcoaxially with hybrid transmission 500. Namely, two degree-of-freedomgear mechanism 2, engine 3 and first motor/generator MG1 are arrangedsuch that axes thereof are aligned with axis O1 of hybrid transmission500. Second motor/generator MG2 is arranged offset from firstmotor/generator MG1 such that axis O2 of second motor/generator MG2 isnon-concentric with and parallel to axis O1, namely, the axis of firstmotor/generator MG1. The arrangement of axes O1 and O2 and axis O3 ofcountershaft 5 and axis O4 of differential 6 is the same as thearrangement thereof in the first through fourth embodiments as shown inFIG. 6. Second motor/generator MG2 is located on one side of plane M,and countershaft 5 is located on an opposite side of plane M.

Two degree-of-freedom gear mechanism 31 includes two simple planetarygear sets 32 and 33 arranged coaxially with hybrid transmission 500.Axes of simple planetary gear sets 32 and 33 are aligned with axis O1 ofhybrid transmission 500. Simple planetary gear set 32 is disposed on afront side close to engine 3, and simple planetary gear set 33 isdisposed on a rear side away from engine 3. Simple planetary gear set 32includes sun gear S1, ring gear R1 and carrier C1 with pinions P1meshing with sun gear S1 and ring gear R1. Simple planetary gear set 33includes sun gear S2, ring gear R2 and carrier C2 with pinions meshingwith sun gear S2 and ring gear R2. Carrier C1 of planetary gear set 32is drivingly connected with ring gear R2 of planetary gear set 33.Carrier C2 of planetary gear set 33 is drivingly connected with ringgear R1 of planetary gear set 32. Planetary gear sets 32 and 33 are thusassociated with each other.

In this embodiment, two degree-of-freedom gear mechanism 31 includesfour rotating members, i.e., sun gear S1, sun gear S2, carrier C1 (ringgear R2), and ring gear R1 (carrier C2), acting as primary elements.FIG. 5B shows a relationship between rotation speeds and rotationdirections of the four rotating members. As shown in FIG. 5B, therotation speeds of the four rotating members are in the following order:sun gear S1, carrier C1 (ring gear R2), ring gear R1 (carrier C2), andsun gear S2.

As shown in FIG. 5B, sun gear S1, carrier C1 (ring gear R2), ring gearR1 (carrier C2) and sun gear S2 of two degree-of-freedom gear mechanism31 are connected with first motor/generator MG1 (first rotor 4R1), inputIN from engine 3, output OUT to a wheel driving system and secondmotor/generator MG2 (second rotor 4R2), respectively. Specifically, asillustrated in FIG. 5A, carrier C1 and ring gear R2 connected withcarrier C1 are connected to transmission input shaft 10. Carrier C1 andring gear R2 serve as an input element indicated by IN in FIG. 5B, towhich the rotation from engine 3 is input. Transmission input shaft 10is disposed coaxially with the crankshaft of engine 3 and drivinglyconnected with the crankshaft via clutch 11. Sun gear S1 is drivinglyconnected with first rotor 4R1 of first motor/generator MG1 via hollowshaft 13 extending from sun gear S1 toward engine 3. Transmission inputshaft 10 extends through sun gear S1, hollow shaft 13 and first rotor4R1 with a clearance between a circumferential outer surface thereof andcircumferential inner surfaces of sun gear S1, hollow shaft 13 and firstrotor 4R1. Sun gear S2 is drivingly connected with second rotor 4R2 ofsecond motor/generator MG2 via central shaft 14 extending from sun gearS2 in a direction toward an opposite side of engine 3. Similar to thefirst embodiment, the driving connection between sun gear S2 and secondrotor 4R2 is established by the gear train constituted of gears 21 and22 which have different diameters and mutually mesh with each other.Ring gear R1 and carrier C2 connected with ring gear R1 are connected tooutput gear 16 via hollow connecting member 15 which is concentricallyarranged with central shaft 14 and acts as an output shaft. Ring gear R1and carrier C2 serve as an output element indicated by OUT in FIG. 5B,which delivers the rotation output to the wheel driving system. Outputgear 16 is rotatably supported on central shaft 14 and axially disposedbetween two degree-of-freedom gear mechanism 31 and the gear train,i.e., gears 21 and 22. Output gear 16 is connected to final drive ringgear 19 via counter gear 17 and final drive pinion 18 provided oncountershaft 5.

An operation of thus-constructed hybrid transmission 500 will beexplained hereinafter. As indicated by lever EV shown in FIG. 5B, when aforward or positive rotation output is transmitted, first and secondmotor/generators MG1 and MG2 operate as motors to produce a power outputfor driving the vehicle without depending on the power output fromengine 3. In this case, the electrical running of the vehicle can beattained only using the power of motor/generators MG1 and MG2.

Next, as indicated by lever MAX shown in FIG. 5B, when the positiverotation speed of motor/generators MG1 and MG2 and the rotation speed ofcarrier C1 and ring gear R2, namely, the rotation output from engine 3,are increased to the largest possible values, respectively, the rotationoutput from ring gear R1 and carrier C2 is enhanced to a maximum.

Further, as indicated by lever REV shown in FIG. 5B, when firstmotor/generator MG1 operates in the positive rotation direction andsecond motor/generator MG2 operates in a reverse rotation direction, thereverse rotation output is transmitted from ring gear R1 and carrier C2to the wheel driving system.

As explained above, in hybrid transmission 500 of this embodiment, firstmotor/generator MG1 is arranged coaxially with hybrid transmission 500and drivingly connected with the rotating member of twodegree-of-freedom gear mechanism 31, i.e., sun gear S1 of simpleplanetary gear set 32, via hollow shaft 13. Second motor/generator MG2is arranged such that axis O2 thereof is offset from axis O1 in parallelrelation thereto, and drivingly connected with the rotating member oftwo degree-of-freedom gear mechanism 31, i.e., sun gear S2 of simpleplanetary gear set 33, via-central shaft 14 which extends from twodegree-of-freedom gear mechanism 31 in such a direction as to come awayfrom engine 3. First motor/generator MG1 is disposed between engine 3and two degree-of-freedom gear mechanism 31 in the direction of axis O1as shown in FIG. 5A. Thus-constructed hybrid transmission 500 of thefifth embodiment has the following effects in addition to the sameeffects as described in the first and second embodiments.

The transmitting device for drivingly connecting sun gear S2 with secondrotor 4R2 of second motor/generator MG2 is not limited to the gear trainincluding gears 21 and 22 and may include wrapping connector drivingmember 23 of the third embodiment and gear train 27 of the fourthembodiment. In such cases, the same effects as described in the thirdand fourth embodiments can be obtained, respectively.

This application is based on a prior Japanese Patent Application No.2003-009206 filed on Jan. 17, 2003. The entire contents of the JapanesePatent Application No. 2003-009206 is hereby incorporated by reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

1. A hybrid transmission comprising: a two degree-of-freedom gearmechanism having a first axis and including at least four rotatingmembers that are associated to rotate about the first axis and include afirst rotating member and a second rotating member, the twodegree-of-freedom gear mechanism being constructed such that, whenrotation conditions of any two of the at least four rotating members aredetermined, rotation conditions of the remainder of the at least fourrotating members are determined depending thereon, the twodegree-of-freedom gear mechanism being adapted for receiving power inputfrom a prime power source and delivering power output from the twodegree-of-freedom gear mechanism; a first motor/generator having asecond axis aligned with the first axis, the first motor/generator beingdrivingly connected with the first rotating member of the twodegree-of-freedom gear mechanism via a hollow shaft; and a secondmotor/generator having a third axis offset from and parallel to thesecond axis, the second motor/generator being drivingly connected withthe second rotating member of the two degree-of-freedom gear mechanismvia a central shaft which extends through the hollow shaft and the firstmotor/generator, the first and second motor/generators being disposed onone side of the two degree-of-freedom gear mechanism in a direction ofthe first axis, the prime power source being disposed on an oppositeside of the two degree-of-freedom gear mechanism in the direction of thefirst axis.
 2. The hybrid transmission as claimed in claim 1, whereinthe second motor/generator has an axial length extending longer than thefirst motor/generator.
 3. The hybrid transmission as claimed in claim 2,wherein the second motor/generator is smaller in diameter than the firstmotor/generator.
 4. The hybrid transmission as claimed in claim 1,further comprising an output shaft having a fourth axis aligned with thefirst axis and a final drive gear that has a fifth axis offset from andparallel to the first axis and is drivingly connected with the outputshaft via a countershaft parallel to the output shaft, the countershaftbeing arranged on one side of a plane containing the fourth axis and thefifth axis, the second motor/generator being arranged on an oppositeside of the plane.
 5. The hybrid transmission as claimed in claim 1,wherein the two degree-of-freedom gear mechanism comprises a compoundplanetary gear set including a single-pinion planetary gear set and adouble-pinion planetary gear set.
 6. The hybrid transmission as claimedin claim 5, wherein the first rotating member is a sun gear of thedouble-pinion planetary gear set, and the second rotating member is asun gear of the single-pinion planetary gear set.
 7. The hybridtransmission as claimed in claim 1, further comprising a transmittingdevice for drivingly connecting the second motor/generator with thecentral shaft.
 8. The hybrid transmission as claimed in claim 7, whereinthe transmitting device comprises a gear train.
 9. The hybridtransmission as claimed in claim 7, wherein the transmitting devicecomprises a wrapping connector driving member.
 10. A hybrid transmissioncomprising: a two degree-of-freedom gear mechanism having a first axisand including at least four rotating members that are associated torotate about the first axis and include a first rotating member and asecond rotating member, the two degree-of-freedom gear mechanism beingconstructed such that, when rotation conditions of any two of the atleast four rotating members are determined, rotation conditions of theremainder of the at least four rotating members are determined dependingthereon, the two degree-of-freedom gear mechanism being adapted forreceiving power input from a prime power source and delivering poweroutput from the two degree-of-freedom gear mechanism; a firstmotor/generator having a second axis aligned with the first axis, thefirst motor/generator being disposed between the two degree-of-freedomgear mechanism and the prime power source and drivingly connected withthe first rotating member of the two degree-of-freedom gear mechanism;and a second motor/generator having a third axis offset from andparallel to the first axis, the second motor/generator being drivinglyconnected with the second rotating member of the two degree-of-freedomgear mechanism via a shaft extending from the second rotating member insuch a direction as to come away from the prime power source.
 11. Thehybrid transmission as claimed in claim 10, wherein the secondmotor/generator has an axial length extending longer than the firstmotor/generator and shorter than the hybrid transmission.
 12. The hybridtransmission as claimed in claim 11, wherein the second motor/generatoris smaller in diameter than the first motor/generator.
 13. The hybridtransmission as claimed in claim 10, further comprising an output shafthaving a fourth axis aligned with the first axis and a final drive gearthat has a fifth axis offset from and parallel to the first axis and isdrivingly connected with the output shaft via a countershaft parallel tothe output shaft, the countershaft being arranged on one side of a planecontaining the fourth axis and the fifth axis, the secondmotor/generator being arranged on an opposite side of the plane.
 14. Thehybrid transmission as claimed in claim 10, wherein the twodegree-of-freedom gear mechanism comprises two simple planetary gearsets.
 15. The hybrid transmission as claimed in claim 14, wherein thefirst and second rotating members are sun gears of the two simpleplanetary gear sets, respectively.
 16. The hybrid transmission asclaimed in claim 10, further comprising a transmitting device fordrivingly connecting the second motor/generator with the shaft.
 17. Thehybrid transmission as claimed in claim 16, wherein the transmittingdevice comprises a gear train.
 18. The hybrid transmission as claimed inclaim 16, wherein the transmitting device comprises a wrapping connectordriving member.
 19. The hybrid transmission as claimed in claim 16,wherein the transmitting device comprises a wrapping connector drivingmember.
 20. A hybrid transmission connected with a prime power source,the hybrid transmission comprising: an input member for receiving powerinput from the prime power source; a two degree-of-freedom gearmechanism having a first axis and including at least four rotatingmembers that are associated to rotate about the first axis and include afirst rotating member and a second rotating member, the twodegree-of-freedom gear mechanism being connected with the input memberand constructed such that, when rotation conditions of any two of the atleast four rotating members are determined, rotation conditions of theremainder of the at least four rotating members are determined dependingthereon; a first motor/generator having a second axis aligned with thefirst axis of the two degree-of-freedom gear mechanism, the firstmotor/generator being drivingly connected with the first rotating memberof the two degree-of-freedom gear mechanism; and a secondmotor/generator having a third axis offset from and parallel to thefirst axis, the second motor/generator being drivingly connected withthe second rotating member of the two degree-of-freedom gear mechanism.21. The hybrid transmission as claimed in claim 20, wherein the twodegree-of-freedom gear mechanism and the first motor/generator arearranged coaxially with the input member, the first and secondmotor/generators being disposed on one side of the two degree-of-freedomgear mechanism in a direction of the first axis, the input member beingdisposed on an opposite side of the two degree-of-freedom gear mechanismin the direction of the first axis.
 22. The hybrid transmission asclaimed in claim 21, wherein further comprising a hollow shaftconnecting the first motor/generator with the first rotating member ofthe two degree-of-freedom gear mechanism, and a central shaft thatextends through the hollow shaft and the first motor/generator andconnects the second motor/generator with the second rotating member ofthe two degree-of-freedom gear mechanism.
 23. The hybrid transmission asclaimed in claim 21, wherein the two degree-of-freedom gear mechanismcomprises a compound planetary gear set including a single-pinionplanetary gear set and a double-pinion planetary gear set.
 24. Thehybrid transmission as claimed in claim 23, wherein the first rotatingmember is a sun gear of the double-pinion planetary gear set, and thesecond rotating member is a sun gear of the single-pinion planetary gearset.
 25. The hybrid transmission as claimed in claim 22, furthercomprising a transmitting device for drivingly connecting the secondmotor/generator with the central shaft.
 26. The hybrid transmission asclaimed in claim 20, wherein the two degree-of-freedom gear mechanismand the first motor/generator are arranged coaxially with the inputmember, the first motor/generator being axially disposed between the twodegree-of-freedom gear mechanism and the input member.
 27. The hybridtransmission as claimed in claim 26, further comprising a shaftconnecting the second motor/generator with the second rotating member ofthe two degree-of-freedom gear mechanism, the shaft extending from thesecond rotating member in such a direction as to come away from theinput member.
 28. The hybrid transmission as claimed in claim 26,wherein the two degree-of-freedom gear mechanism comprises two simpleplanetary gear sets.
 29. The hybrid transmission as claimed in claim 28,wherein the first and second rotating members are sun gears of the twosimple planetary gear sets, respectively.
 30. The hybrid transmission asclaimed in claim 27, further comprising a transmitting device fordrivingly connecting the second motor/generator with the shaft.
 31. Thehybrid transmission as claimed in claim 26, wherein the secondmotor/generator has an axial length extending longer than the firstmotor/generator.
 32. The hybrid transmission as claimed in claim 31,wherein the second motor/generator has an axial length extending shorterthan the hybrid transmission.
 33. The hybrid transmission as claimed inclaim 31, wherein the second motor/generator is smaller in diameter thanthe first motor/generator.
 34. The hybrid transmission as claimed inclaim 26, further comprising an output shaft having a fourth axisaligned with the first axis and a final drive gear that has a fifth axisoffset from and parallel to the first axis and is drivingly connectedwith the output shaft via a countershaft parallel to the output shaft,the countershaft being arranged on one side of a plane containing thefourth axis and the fifth axis, the second motor/generator beingarranged on an opposite side of the plane.
 35. The hybrid transmissionas claimed in claim 30, wherein the transmitting device comprises a geartrain.
 36. The hybrid transmission as claimed in claim 30, wherein thetransmitting device comprises a wrapping connector driving member.